The present invention generally relates to die casting of motor or engine blocks and more particularly relates to cooling aspects of such motor blocks.
The use of the lost foam casting process in the casting of motor blocks has resulted in substantial advantages in terms of manufacturing costs and the resulting motor. One of the distinct advantages is that a one piece casting can be manufactured using such a process wherein the casting includes components that previously had to be separately made and subsequently assembled during the manufacturing process. For example, the lost foam casting process can result in an exhaust manifold that is integrally formed with the motor block. The process also permits a motor to be made that is compact in design, but yet still has the desired power output. With a compact design, extreme care must be taken to provide adequate cooling of the motor block, particularly given the high heat output that occurs when such powerful motors are running at speed.
In a typical outboard motor having multiple cylinders, it is desirable to provide a cylinder bore geometry that is as round as possible and one of the factors which influences the roundness of the bore is the temperature uniformity in the cylinder wall and the adjacent area.
One method for achieving a uniform temperature distribution is to design the cylinder or motor block with a deep water jacket in the cylinder bore area. However, because of the advent of the use of helical transfer passages which extend the cylinder wall outwardly beyond the cylindrical shape of the cylinder bore and the necessity of having cylinders adjacent one another in cylinder banks, it is not always possible to extend the water jacket as deeply along the cylinder wall as is desired. Such a situation can result in cylinder bore distortion if there exists a hot area adjacent the cylinder bore that has not properly cooled.
In certain motor designs, including commercially available V-bank six-cylinder outboard motors which have two banks of three cylinders, there is a location that is difficult to cool because of the presence of intake ports and helical transfer passages in the immediate area between adjacent cylinders of each bank. This hot area has tended to pinch the center cylinder of a three cylinder bank which tended to force it out of round which can cause a premature wearing of the motor piston.
In certain commercially available engines, cooling of this area has been provided by drilling holes in the casting in this area. However, with improved engine designs which utilize the lost foam casting process, coupled with the use of the helical transfer passages, there is not sufficient room or access to easily accomplish such drilling, or if it is attempted, the desired wall thickness of the cylinder walls cannot be maintained with a single drilling. Also, because of typical helix angles that are present on most intake passages for two stroke motors, multiple drilling must be done at oblique angles which are difficult to make in production and are therefore expensive.
Accordingly, it is a primary object of the present invention to provide an improved cast motor block which includes a cooling passage in the area between adjacent cylinders in a motor of the type which has helical transfer passages and integrally cast intake ports.
Yet another object of the present invention is to provide such a motor block that has cooling passages between adjacent cylinders and between helical transfer passages in the immediately adjacent area, which can be integrally cast using a lost foam casting process.